In 2014, astronomers using the Pan-STARRS telescope in Hawaii discovered an asteroid doing something strange: orbiting the Sun clockwise, unlike all the planets and most asteroids in the solar system, which orbit counter-clockwise. The object shares a similar orbit to Jupiter’s – similar, that is, except for its “retrograde” direction of motion.

Earlier this year, researchers at Côte d'Azur Observatory in France and São Paulo State University in Brazil published a paper offering an intriguing explanation: that BZ509 is an interstellar visitor, which arrived during the solar system's infancy, perhaps 4.5 billion years ago, and was captured into a remarkably stable orbit thanks to Jupiter's influence.

If BZ509 did indeed originate from an alien star system, a tantalizing – although unlikely – possibility is that it was engineered by intelligent life-forms and sent intentionally to our newly-forming Solar System. Breakthrough Listen is in a unique position to observe the object and place stringent limits on any radio emission from putative transmitters on its surface.

Beginning on Wednesday, 30 May, Listen will be using two receivers on the Parkes 64-m telescope in New South Wales, Australia, to observe BZ509: the ‘multibeam’ observing over 1.2 – 1.5 GHz, and the brand new 'ultra-wideband' receiver observing over 0.7 – 4 GHz. With these receivers, Listen could detect a 1 watt isotropic narrowband transmitter (the same power level as a cell phone) on the surface of BZ509 after no more than five minutes’ observation. The campaign will consist of several observing sessions over the following week.

The 2015 BZ509 asteroid is approximately 4.6 Astronomical Units, or 430 million miles, from Earth, with celestial J2000 coordinates (RA 20 hours, declination -15 degrees), making it a Southern hemisphere source. Its orbital period is 11.64 years; it will not be in perihelion (its closest approach to the Sun) for another ~10 years.

It remains overwhelmingly likely that BZ509 is of natural origin. But observations of it provide another opportunity to exercise BL’s technical capabilities – especially in observing nearby, fast-moving targets.

Meanwhile, following the discovery of the interstellar asteroid ‘Oumuamua in 2017, this is further evidence that exchange of material between planetary systems might be more common than we thought. This provides renewed motivation to consider theories like panspermia – which postulates that life is transported between the stars by comets, asteroids and other travellers; and even the possibility that an artifact of a distant technological civilization might have made its way to our solar system at some point.

After all, if human beings are capable of sending our technology to other stars – as intended by the Breakthrough Starshot program – why couldn’t another intelligent civilization do the same thing?